The colours represent different percentile groups: dark green is the 90-100% best. Light green is 75% >. Then we have orange, yellow, pink and red. Red is really bad. Mind your wallet at any time.
In the Americas the by far most corrupt countries are Haiti and Venezuela. Venezuela always had big corruption problems, but now, as we can see from the last post and 90% of the others, things have got to new (lower) levels. The least corrupt countries in the Americas are Canada and the USA. Venezuela has more in common with the most corrupt countries in Africa than anything else. There are quite some countries in the poorest continent on Earth with much better accountability standards than in Venezuela.
(there is a wee error in the explanation: Ukraine belongs to the pink, not the red percentile group)
In Europe you can see the worst countries are Russia and Belarus. I was surprised Moldova did not make it to the worst here, but perhaps it does in other parameters like rule of law.
There are also important differences between countries in the same rank. There is a difference between the US, Belgium or France and, say, Norway or Finland, all in dark green here. Sleaze in Brazil or Colombia is much higher than in Costa Rica and you have more issues in Bulgaria or Romania than in the Czech Republic. There are more problems with corruption control in some regions within a nation (yes, clichés are sometimes based on reality, as we can see in Italy, Spain and Belgium).
Ps. I know, I did not colour the Asian part of Russia or Turkey or Greenland or Armenia-Georgia-Azerbaijan. Perhaps I do it later on.